1. Field of the Invention
The present invention relates to a monitoring and control apparatus for monitoring and controlling facilities and equipment of a plant and, more particularly, to a monitoring and control apparatus provided with means for verifying healthiness of a control processing unit within the apparatus.
2. Description of the Background Art
One known conventional system of this kind is a measurement control system disclosed in Japanese Laid-open Patent Application No. 1987-276991, for example. In this measurement control system, a detecting end device and an operating end device provided on-site are connected to a control unit by transmission lines, and the control unit collects measurement information from the detecting end device and controls the operating end device by performing specific control processing operation. The measurement control system includes a data input unit and a data display unit provided on the outside of the control unit, and when the control unit performs its own test, the control unit causes the data input unit to transmit simulated data for testing, processes the simulated data by a control processing program of the control unit and displays a test result on the data display unit.
Another known system of this kind is a conventional test support system described in Japanese Laid-open Patent Application No. 1997-114689, for example. The test support system for testing programmable logic controllers (PLCs) which are interconnected on a communication network and serve as constituent elements of a distributed system is provided with a PLC emulator, instead of the PLCs on the network, for simulating transmission and reception of data to and from a group of personal computers and a data storage function.
In the system of Japanese Laid-open Patent Application No. 1987-276991 cited above, transmission and reception through the transmission line between the control unit and the on-site devices are interrupted or switched at the time of testing and, then, the simulated data is generated and input into the control unit and the test result is output. Even if the system is so configured as to automatically generate the simulated data as described in Japanese Laid-open Patent Application No. 1997-114689 cited above, it is necessary to provide an external device for inputting and outputting the simulated data to and from the control unit. Furthermore, it is not easy to switch the transmit/receive operation between the control unit and the on-site devices which are actually used during real operation to transmit/receive operation between the control unit and the external device for inputting and outputting the simulated data, and this makes it difficult to achieve a reduction in size and simplification of the system configuration.